1. Field of the Invention
This invention relates to a novel method of synthesizing perfluorodialdehydes and to novel intermediates useful in the synthesis thereof.
2. Description of the Prior Art
Though various procedures have been proposed for synthesizing aldehydes, in general, they have not always been successful when applied to highly fluorinated compounds because of the relatively inert nature of fluorinated compounds as compared to their hydrocarbon counterparts. Usually, the synthesis of perfluoromonoaldehydes has been accomplished by the lithium aluminum hydride reduction of the corresponding esters at low temperatures as described by D. R. Husted and A. H. Ahlbrecht, J. Amer. Soc., 74, p. 5422 (1952). Inverse addition has been reported to improve yields as discussed by O. R. Pierce and T. G. Kane, ibid., 76, p. 300 (1954) and by M. Braid, H. Iserson and F. E. Lawlor, ibid., 76, p. 4027 (1954).
Although we anticipated no difficulty in the preparation of perfluorodialdehydes by the standard methods used for the perfluoromonoaldehydes, only traces of the desired product could be detected from the lithium aluminum hydride reduction of dimethyl perfluoroadipate in ether at either 0.degree. C. or -70.degree. C. Equally unsuccessful was the attempted reduction of perfluoroadipoyl chloride in tetrahydrofuran using lithium tri-t-butoxyaluminum hydride.
U.S. Pat. No. 3,344,193 discloses the use of catalytic reduction in the preparation of perfluorinated dialdehydes, such as, 2,2,3,3,4,4-hexafluoro-1,5-pentanedialdehyde. As described therein, the fluorinated dialdehydes are synthesized from the corresponding diacid halides by catalytic reduction preferably using a palladium on carbon catalyst and particularly a poisoned catalyst of this type.
In one aspect, the present invention is concerned with a method of preparing perfluorodialdehydes. In another aspect, the present invention is concerned with intermediates useful in the production of perfluorodialdehydes and the preparation of the intermediates.